Displacement sensor for a living body

Abstract

A displacement sensor for a living body provides an improved stethoscope and/or cardiogram. The apparatus has a diaphragm which is placed on the surface of a living body, a permanent magnet located on the diaphragm, an inductor arrangement located adjacent to the permanent magnet so that the saturable inductor changes its inductance according to movement or vibration of the magnet, a processor circuit which processes the inductance variation in the inductors to provide an electrical output signal for visual display and recording purposes, and a hollow sound tube which introduces an acoustic vibration sound of the diaphragm to the ears of a doctor. The present apparatus provides not only acoustic sound output but also visual display and a printed copy as a mechanocardiogram sensor.

What is claimed is: 
     
       1. A displacement sensor comprising: a diaphragm which is adapted to be placed on a living body,   a magnetic pole (M) fixed on said diaphragm,   a pair of saturable inductors (24,25) positioned close to said magnetic pole,   each of said saturable inductors (24,25) comprising a plurality of inductors having saturable cores and coils, each coil wound on said core,   said coils being positioned radially on a plane which is perpendicular to said diaphragm, and   said coils being connected in series alternately.   
     
     
       2. A displacement sensor according to claim 1, further comprising processor means (6) for supplying alternating signals to said saturable inductors (24,25) to measure inductance of the inductors, thereby reflecting displacement of said magnetic pole. 
     
     
       3. A displacement sensor according to claim 1, further comprising processor means for processing output signals of said inductors. 
     
     
       4. A displacement sensor according to claim 3, wherein said processor means comprises a pair of transistors; a pair of parallel circuits of a capacitor and a resistor coupled between a base of one transistor and a collector of the other transistor, the collector of each transistor being coupled with an end of each inductor (24, 25), a junction point of series connected inductors (24, 25) being coupled with a power supply of frequency f, a balance circuit bridging emitters of said transistors, and a filter coupled across said emitters to provide an output signal. 
     
     
       5. A displacement sensor according to claim 4, wherein said frequency f is in the range between 100 kHz and 500 kHz. 
     
     
       6. A displacement sensor according to claim 4, wherein said filter is a low-pass filter. 
     
     
       7. A displacement sensor according to claim 1, further comprising a hollow tube for coupling acoustically said diaphragm with ears of a user. 
     
     
       8. A displacement sensor according to claim 1, wherein each of said coils is wound on a linear magnetic core made of amorphous material. 
     
     
       9. A displacement sensor according to claim 1, wherein said magnetic pole is a permanent magnet. 
     
     
       10. A displacement sensor according to claim 1, wherein each of said inductors (24, 25) has 12 series connected inductors. 
     
     
       11. A displacement sensor according to claim 1, wherein the length between said diaphragm and said inductors is adjustable.